docs: def at(self, timestamp):
          """
          Force the create date of an object to be at a certain time; This
          method can be invoked only on a freshly created Versionable object.
          It must not have been cloned yet. Raises a SuspiciousOperation
          exception, otherwise.
          :param timestamp: a datetime.datetime instance
          """
          # Ensure, it's not a historic item
          if not self.is_current:
              raise SuspiciousOperation(
                  "Cannot relocate this Versionable instance in time, since it "
                  "is a historical item")
          # Ensure it's not a versioned item (that would lead to some ugly
          # situations...
          if not self.version_birth_date == self.version_start_date:
              raise SuspiciousOperation(
                  "Cannot relocate this Versionable instance in time, since it "
                  "is a versioned instance")
          # Ensure the argument is really a timestamp
          if not isinstance(timestamp, datetime.datetime):
              raise ValueError("This is not a datetime.datetime timestamp")
          self.version_birth_date = self.version_start_date = timestamp
          return self